Prior image area identification systems were typically designed to function with fiducial markings that were clearly delineated and easily distinguishable from other image information. The fiducial markings are used to determine the registration of the document for the purpose of accurately determining the location of predetermined positions on the image. The fiducial markings employed may be markings specifically employed for the recognition process or they may be known easily identifiable objects that comprise a part of the image. These fiducial markings are typically regular patterns placed along the edges or in the corners of the image being scanned and suffer the disadvantage of obtrusiveness. Furthermore, these prior systems perform registration of an image under the assumption that the scanned image will be largely undistorted and free of noise. However, distortions and modifications to a scanned image are common. These distortions can be introduced either on the original item being scanned, via the scanning process or in transmission of the scanned image. Exemplary causes of such distortions are smudges on the original item being scanned, a slipping feed mechanism, a dirty scanner, or errors in facsimile (FAX) transmission over a noisy telephone line.
In some instances, distortions to the scanned image are non-linear. This type of distortion can arise, for example, if the surface being scanned is being turned during the scanning process. A single skew and offset correction is insufficient to correct for such a distortion. One prior system suggests using multiple fiducial markings spaced throughout the image surface to compensate for non-linear distortions introduced in the scanned image with respect to an ideal image by using piecewise linear approximation techniques. However, this system requires a controlled second scan of the actual image to generate a compensated image. It is impossible to obtain such a controlled second scan in many image scanning applications. Also, use of this prior system is limited to applications wherein all fiducial markings are present in the scanned image and wherein all markings are successfully detected. Furthermore, this prior system is unable to function satisfactorily in the event that a particular area of the image is falsely detected as a fiducial marking.